Meeting Abstract
78.3 Friday, Jan. 7 Renegade clams: Marine bivalves follow neither Bergmann’s Rule nor its converse BERKE, S K*; JABLONSKI, D; KRUG, A Z; TOMASOVYCH, A; VALENTINE, J W; Univ. of Chicago; Univ. of Chicago; Univ. of Chicago; Univ. of Chicago; Univ of California, Berkeley skberke@gmail.com
Bergmann’s Rule describes the tendency for taxa to get larger with latitude. Although many taxa follow this rule (e.g. birds and mammals), many other taxa become smaller at high latitudes, following the converse to Bergmann’s Rule (e.g. insects). While such global size patterns are well-known for terrestrial organisms, size patterns for marine organisms have received far less attention. We analyzed body sizes for 2596 species representing 1002 genera and 76 families of living marine bivalves worldwide. The means and variances of bivalve size distributions are surprisingly constant across provinces and climate zones. Strikingly, however, the Antarctic bivalve fauna is significantly smaller than faunas from other provinces, including the Arctic. This shift towards smaller sizes has occurred since the Eocene, when the poles were warmer and Antarctic body sizes were similar to the rest of the world. To test whether environmental factors such as temperature or productivity drive the difference between the poles, we assessed the relationships between body size and both sea surface temperature and net primary productivity for each province. While Antarctica and the Arctic experience similar SST regimes, preliminary data suggest that Antarctica supports lower mean annual NPP overall than any other province. Terrestrial body-size gradients are thought to be related to temperature for endotherms, and some combination of temperature and productivity for ectotherms. These data suggest that temperature plays little direct role in shaping size distributions for marine invertebrates, which are strikingly similar across climate zones. Smaller Antarctic sizes suggest that productivity may be more important, though perhaps only below some threshold value.
